In order to connect an integrated circuit formed in an element region of a semiconductor substrate to a circuit (an external circuit) provided on the outside of the substrate, a pad electrode has been formed in a non-element region in the peripheral edge portion of the semiconductor substrate. The pad electrode is electrically connected to the integrated circuit, and furthermore, is electrically connected to the external circuit through a lead.
The connection of the pad electrode and the lead is performed through a bump (projection) electrode. This kind of bump electrode has conventionally been formed by electrolytic plating such as gold, solder and the like.
FIGS. 18A to 18E are sectional views showing steps of a method for forming a bump electrode according to the prior art. In order to form the bump electrode, first of all, a plurality of pad electrodes 83 (only one of them is shown in the drawing) made of Al are formed in a non-element region covered with an insulating film 82 in the peripheral edge portion of a semiconductor substrate 81 as shown in FIG. 18A.
More specifically, for example, an Al film is formed by using a sputtering method, and the Al film is then processed by photolithography and RIE, thereby forming the pad electrode 83. The pad electrode 83 is electrically connected to a semiconductor device constituting an integrated circuit (not shown) which is formed on the semiconductor substrate 81.
As shown in FIG. 18A, next, an interlayer dielectric film 84 is formed over the whole surface of the semiconductor substrate 81, and the interlayer dielectric film 84 provided on the pad electrode 83 is then removed selectively by etching, thereby forming an opening.
As shown in FIG. 18A, then, a Ti film 85, an Ni film 86 and a Pd film 87, which are conductive films necessary for electrolytic plating, are sequentially formed by using the sputtering method, for example, so as to cover the exposed pad electrode 83 and the interlayer dielectric film 84.
The Ti film 85 is a barrier film of a bump electrode material, the Ni film 86 is a contact film to perform a contact of the pad electrode 83 with the bump electrode, and the Pd film 87 is an oxidation inhibiting film for inhibiting the oxidation of the Ni film 86.
As shown in FIG. 18B, thereafter, a photoresist pattern 88 is formed. The photoresist pattern 88 has a thickness of about 20 xcexcm and is provided with an opening in a region where the bump electrode is to be formed.
As shown in FIG. 18C, subsequently, the films 85 to 87 are electrically charged by a current-carrying pin to perform the electrolytic plating, for example. Thus, a bump electrode 89 made of gold or solder is selectively formed in the opening. In this case, it is necessary to previously cover, with an insulator, a region which should not be subjected to the electrolytic plating, for example, the back side of the semiconductor substrate 81.
As shown in FIG. 18D, next, the photoresist pattern 88 is taken away, and the films 85 to 87 are then subjected to wet etching by using the bump electrode 89 as a mask. Thus, the films 85 to 87 are caused to remain under the bump electrode 89, thereby insulating the bump electrodes.
As shown in FIG. 18E, finally, the bump electrode 89 is subjected to reflow by performing heating while applying a flux.
However, such a method for forming the bump electrode 89 has the following drawbacks.
First of all, the electrolytic plating is used for the formation of the bump electrode 89. The electrolytic plating requires a large number of steps. For this reason, there is a problem in that the number of steps is large.
At a wet etching step for the various films 85 to 87 which have been subjected to the sputtering prior to the plating, a wet etching step and a washing step should be performed several times according to the kind of the film, and a vast amount of water is required.
Recently, the pad electrode 83 has also been formed more finely with an increase in the fineness of the element. Therefore, there are some cases where an antireflection film such as a TiN film to prevent reflection during exposure at a lithography step is formed on an Al film acting as the pad electrode 83.
Although the TiN film is effective as a barrier metal, it has poor adhesion to the bump electrode made of metal such as solder, gold or the like. For this reason, after the Al film is processed to form the pad electrode 82, the TiN film should be removed. Consequently, the number of steps tends to be increased still more.
Moreover, a resist pattern to be used at the etching step which is an ordinary semiconductor process has a thickness of several xcexcm, while the resist pattern 88 to be used at the plating step has a great thickness of 20 xcexc as described above. For this reason, there is a problem in that the photolithography step for forming the resist pattern 88 will be hard to perform in the future.
Moreover, in the case where a semiconductor device having the resist pattern 88 formed therein is immersed in a strongly acidic plating bath, the resist pattern 88 is eluted as an organic impurity into the plating bath at the electrolytic plating step so that the composition balance of a plating solution is lost.
As a result, a variation in the reflow reaction temperature of the bump electrode 89 is generated at a reflow step of the bump electrode 89 and a mounting connection step thereof. Consequently, there is a problem in that the reliability and yield of the connection is deteriorated.
By the high functionality of the element and various mounting steps, a reduction in the size of the pad electrode and an increase in the number of the pad electrodes are accelerated. Therefore, a reduction in the above-mentioned variation will be increasingly significant in the future in order to keep the reliability of the pad electrode 89.
In order to eliminate the above-mentioned drawbacks, there has been known a method in which a metallic ball such as a solder ball, a gold ball or the like is provided on an Al pad electrode and is then pressure welded and melted to form a bump electrode.
However, in the case where the solder ball is provided on the Al electrode pad, a barrier film and an adhesion layer are to be formed,in order to prevent Sn constituting the solder ball from being diffused into the Al electrode pad. In this respect, the number of steps is increased in the same manner as in plating film formation.
As one of metal film forming methods, a fine particle film forming method has been known and application to a part of the method to a process has been investigated. As a method for application to a mounting technique, there has been investigated a method for forming a bump electrode made of fine particles of gold (Au) by depositing the Au fine particles on a pad electrode.
In the case of this method, it is necessary to deposit a large quantity of Au fine particles in order to form a bump electrode having a required thickness. Under the existing conditions, however, a deposition rate or the like is insufficient. Therefore, there is a problem in that such a method does not correspond to a real process. In other words, there has not been a real electrode structure using a conductive fine particle film.
It is an object of the present invention to provide a semiconductor substrate having a real electrode structure using a conductive fine particle film and a method for manufacturing the semiconductor substrate, and a fine particle film forming apparatus and method which is effective in the formation of a fine particle film such as a conductive fine particle film.
The present invention provides a fine particle film forming apparatus comprising a vessel having a gas inlet for introducing a gas therein provided on one of ends thereof and having a gas blow-off nozzle for blowing off a gas containing fine particles to an outside provided on the other end thereof, a gas flow forming portion for forming a constant gas flow in the vessel from the gas inlet toward the gas blow-off nozzle, a target provided in the vessel for acting as a fine particle source, a fine particle generating portion for irradiating light on a main surface of the target, thereby discharging a component of the target into the gas flow to form the fine particles made of the component in the gas flow, and a moving portion for moving the vessel.
Preferably, the moving portion can cause the gas blow-off nozzle and the surface of the substrate where the fine particles are formed to be positioned at a desirable interval, thereby relatively moving the vessel with respect to the substrate. Furthermore, it is preferable that the magnetic forming portion for forming a magnetic field in the region on the substrate should be provided. A magnetic field may be formed in the region on the substrate and other regions. In short, it is sufficient that the magnetic field can affect the formation of the fine particle film.
Moreover, the present invention provides a method for forming a fine particle film, comprising the steps of preparing a target as a fine particle source, irradiating light on a main surface of the target, thereby discharging a component of the target to an outside, forming fine particles from the discharged component, and carrying the fine particles on a gas flow to a surface of a substrate, thereby forming a fine particle film made of the fine particles on the substrate.
Furthermore, the present invention provides another method for forming a fine particle film, comprising the steps of preparing a substrate, and supplying a gas or medium containing fine particles having a magnetism to the substrate and forming a magnetic field on the substrate, thereby forming a fine particle film on the substrate.
It is desirable that the magnetic field should be formed in the vicinity of the region on the substrate. The magnetic field can also be formed in the vicinity of the region on the substrate and other regions. In short, it is sufficient that the magnetic field can affect the formation of the fine particle film. More specifically, it is sufficient that a distribution of the magnetic field is controlled, thereby increasing an acceleration of the gas or medium in a direction of the substrate. The increase in the acceleration means at least one of an increase in the speed of the gas or medium and an increase in the amount of the gas or medium running at the same speed in the direction of the substrate.
The present invention provides a semiconductor device comprising a semiconductor substrate, and an electrode structure provided on the semiconductor substrate and constituted by a first electrode provided on the semiconductor substrate, a conductive fine particle film provided on the first electrode and made of conductive fine particles, and a second electrode provided on the conductive fine particle film.
Moreover the present invention provides another semiconductor device comprising a semiconductor substrate, and an electrode structure provided on the semiconductor substrate and constituted by a first electrode provided on the semiconductor substrate, a barrier film provided on the first electrode, a conductive fine particle film provided on the barrier film and made of conductive fine particles, and a second electrode provided on the conductive fine particle film.
Furthermore, the present invention provides yet another semiconductor device comprising a semiconductor substrate, and a bump electrode structure provided on the semiconductor substrate and constituted by a first electrode provided on the semiconductor substrate, a conductive fine particle film acting as a barrier film and an adhesion layer which is provided on the first electrode and is made of conductive fine particles, and a second electrode provided on the conductive fine particle film.
The present invention provides a method for manufacturing a semiconductor device comprising the steps of forming a pad electrode on a semiconductor substrate, forming an insulating film on the semiconductor substrate on a side where the pad electrode is formed, removing the insulating film provided on the pad electrode, thereby forming, on the insulating film, an opening reaching the pad electrode, forming, on a bottom of the opening, a conductive fine particle film as an adhesion layer and a barrier film that is made of conductive fine particles, providing a bump electrode on the conductive fine particle film, and joining the bump electrode to the conductive fine particle film.
The present invention provides another method for manufacturing a semiconductor device comprising the steps of forming, on a semiconductor substrate, a pad electrode having a top face covered with a barrier film, forming an insulating film on the semiconductor substrate on a side where the pad electrode is formed, removing the insulating film provided on the barrier film, thereby forming, on the insulating film, an opening reaching the barrier film, forming, on a bottom of the opening, a conductive fine particle film as an adhesion layer that is made of conductive fine particles, providing a bump electrode on the conductive fine particle film, and joining the bump electrode to the conductive fine particle film.
The present invention provides yet another method for manufacturing a semiconductor device comprising the steps of forming a pad electrode on a semiconductor substrate, forming an insulating film on the semiconductor substrate on a side where the pad electrode is formed, removing the insulating film provided on the pad electrode, thereby forming, on the insulating film, an opening reaching the pad electrode, forming a barrier film on a whole surface of the substrate on a side where the opening is formed, forming, on the barrier film in the opening, a conductive fine particle film as an adhesion layer which is made of conductive fine particles, providing a bump electrode on the conductive fine particle film, joining the bump electrode to the conductive fine particle film, and removing the barrier film on an outside of the opening.
It is preferable that the method for manufacturing a semiconductor device should further comprise the step of removing a natural oxide film formed on the conductive fine particle film or a natural oxide film formed on the conductive fine particle film and the bump electrode.
The natural oxide film formed on the conductive fine particle film may be removed during or after the formation of the conductive fine particle film or during and after the formation of the conductive fine particle film.
Moreover, the conductive fine particle film and the natural oxide film of the bump electrode may be removed at separate steps respectively or may be removed at the same time.
Furthermore, the natural oxide film is removed by a heat treatment (a heating treatment), for example.
More specifically, the removal is carried out by the heat treatment in a vacuum atmosphere, an inactive gas atmosphere, a reducing gas atmosphere, or a gas atmosphere containing H2 and a flux. Examples of other removing methods include a method using a reverse sputtering method.
Similarly, it is preferable that the natural oxide film formed on the pad electrode, the barrier film or both of them should be removed.
The natural oxide film formed on the pad electrode and the barrier film may be removed before or during the formation of the conductive fine particle film, or before and during the formation of the conductive fine particle film. Moreover, the same removing method as that of the conductive fine particle film is used, for example.
According to the present invention, the conductive fine particle film is not used for the electrode but is utilized as the contact film and the barrier film to be inserted between the electrodes. Since such films are much thinner than the electrode, they do not make troubles on a deposition rate but correspond to a real process. Accordingly, it is possible to implement a real electrode structure using the conductive fine particle film.
According to the present invention, furthermore, the fine particles can selectively be deposited more easily in the predetermined region. Therefore, the fine particle film can selectively be formed easily in the predetermined region. According to the present invention, therefore, it is possible to prevent the number of steps from being increased when forming the electrode structure according to the present invention.
According to the present invention, moreover, the kinetic energy of the fine particles colliding with the substrate can be increased by utilizing the magnetic field. As a result, it is possible to form fine particles film having a higher density.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.